Hot shearing devices of this kind in general are combined with plants for manufacture of hot-pressed or forged products from non-ferrous metals. For the production of pressed aluminum foils or sheet material, for instance, extruded aluminum rods are taken from store and placed in a heater until where they are heated to a certain processing temperature and are subsequently transported to a hot shearing apparatus. In this hot shearing apparatus the heated rods are cut to certain lengths and then supplied to a molding machine, for example an extruder.
Billet hot shearing apparatus normally have a fixed front shearing bushing and a rear shearing bushing which is vertically movable, a transport means for advancing the rods into the shearing bushing and for returning the remainder of the rod into the heater unit, and an abutment means for limiting the advance and initiating the shearing process. Moreover, known hot shearing devices comprise hydraulic drive means to produce the shear forces, a receptacle for the sheared billets, and ejector and transfer devices for removing the sheared billets from the shearing apparatus. The known hot shearing apparatus for billets have disadvantages which greatly limit their field of application and availability. For instance, it is a disadvantage that the length of the shearing bushings is much greater than their diameter. This results in a great channel length which makes it likely for the billets, which are often curved or bent due to the heating, to contact the inner wall of the channel. Any such contact, however, causes friction which impairs the transportation. As the hot aluminum has a tendency to adhere firmly to the faces of the shearing bushings the transportation of the rods through the shearing bushings often is rendered so difficult that the rods can no longer pass through the bushing openings without trouble. In such cases the entire plant must be shut down and cleaned.
The inventor discovered that even a larger inner diameter of the bushings, by which the clearance between the billets or bars and the bushings would be enlarged, does not help to eliminate the above mentioned difficulties.
Contacting of the bushings walls, in particular by distorted billets or rods cannot be avoided by the selection of larger bushing diameters which are selected in accordance with the respective maximum curvature of the billets or rods because the billets or rods are deformed to such an extent during the first shearing that the larger parts of their circumference engages the inner wall of the bushing. Thus the clearance mentioned is eliminated for the second shearing already and for all further shearing processes to which the respective billet is subjected. Moreover, further serious disadvantages result from the choice of a larger inner diameter of the bushings. For instance, the inclination or tilting of the billets or rods with respect to the longitudinal axis during the shearing process will be the larger the larger the clearance between the diameters is chosen to be. This will produce an oblique cut, i.e. a cut which does not extend vertically to the longitudinal axis of the billet or rod. Furthermore, the diameter of the billet at the sheared end because more deformed by the upsetting of material in the case of a large clearance and becomes so enlarged that also the diameter of the recipient of the extruder or extrusion press for tubes must be selected to be so much larger. The resulting disadvantages regarding air pockets and reduced specific pressing forces are wellknown.
Known hot shearing devices for billets include abutment means which have sensor pins to release the shearing process when contacted by the billet end. The sensor pin may enter into the material of the billets or rods which was softened by the heating and may considerably obstruct the transverse displacement required during shearing of the billet sections to be severed. This may also result in abrasion or sticking of the pins, thus disturbing the proper functioning of the plant.
Another disadvantage of the known hot shearing apparatus resides in the lateral transfer of the billets which frequently consist of two rod rests from the hot shearing apparatus to the loading means of the press or to an intermediate station when the part sections of the billets are dumped to the side out of the take-up means.